The hippocampus, a structure inside the brain, shrinks after psychological trauma, which hints that a pharmaceutical cure may address post-traumatic stress disorder.

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“Hippocampal shrinkage,” of all the terrible-sounding human ailments, is a common condition among post-traumatic stress disorder patients. It means a vital part of the brain is too small. The shrinkage helps to explain flashbacks, but what hasn’t been clear until recently is whether a smaller hippocampus leaves a person predisposed to PTSD or whether shrinkage results from the stress (of, say, combat, or a rape, or a natural disaster).

“The hippocampus plays a big role in storing memories, but it’s also important in recalling them,” says Ulrike Schmidt, a senior psychiatrist and research group leader at the Max Planck Institute of Psychiatry in Munich, “and this recall is obviously disrupted in PTSD patients.”

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The hippocampus, which is Greek for “seahorse,” is a paired structure tucked inside each temporal lobe and shaped, in fact, like a pair of seahorses. It helps to store and release memory. A damaged hippocampus causes weird things to happen, like a damaged hard drive, and Schmidt gives the example of a rape victim who suffers a flashback after seeing a stranger who resembles the rapist.

“That means the recall is too fast and too unspecific,” she says. “The hippocampus isn’t functioning well. But we don’t quite understand how that’s related to the smaller size.”

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One much-cited 2002 study of twins showed that some people who wind up with PTSD have smaller hippocampi to start with. That pointed to a small hippocampus as a biological vulnerability. A soldier in combat needs quick memory feedback to know when he’s in trouble, and some recent work suggests that a hobbled hippocampus can blur this danger response, leading the brain to notice more cues than necessary and causing the soldier, in effect, to freak out.

Schmidt and her colleagues are studying hippocampal shrinkage, as well as living conditions that can allow the brain to recover. None of it points, yet, to a pharmaceutical cure, in part because PTSD is a massively complex condition that manifests itself on a number of physical levels (which I’ll write about in upcoming columns). But Schmidt says most modern molecular research is aimed at finding a drug.

What nevertheless helps is human interaction. “For years, people with PTSD were treated as weaklings who were not really ill,” Schmidt says. “But we’ve learned that you can’t just leave them alone. They need to know that it’s a recognized disorder. They are not weak; they’re sick, they have a spiritual wound. ... And it’s important that they aren’t treated like outsiders, which is how many soldiers were treated in Europe in the ’40s and ’50s.”

Hang on — spiritual wound? Is that a scientific category?

“For me, it all goes wonderfully together,” she says. “The brain is a marvelous chemical construction set. Every thought, and every feeling, is a molecular reaction. That doesn’t mean we can’t also understand it poetically or express it in phrases like ‘spiritual wound.’ That’s what it is. A traumatic experience can leave a defect in this molecular system. … Of course, it’s two separate languages we’re using, but for me, there’s no contradiction.”